Last week the bank commenced sending out letters to the customers, who were charged incorrect interest rates through their mortgage offset accounts due to processing errors by the bank.

Some of the errors dated back to 2003, and occurred because key processes were carried out manually, leaving the door open to human error.

Customer complaints first alerted the bank to problems with the offset accounts in 2010, which then led to a four-year review led by PwC.

The head of the bank’s Australian operations, Phil Chronican, said the bank had also decided to put all of its products under the microscope as part of a separate review taking in several million accounts.

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